Computer systems use various methods of receiving information from a user, such as serial I/O ports, parallel I/O ports, keyboards, bus expansion slots and cartridge slots. If a computer program requires the ability to receive analog inputs, a circuit is required to convert the analog inputs to a digital value and to present that value to the computer through one of its methods of input. In addition, if a computer requires the ability to sense the position of a switch, a circuit is required to convert the switch position to a digital value and to present that value to the computer through one of its methods of input. While computer interface circuits are known, the present invention utilizes a novel arrangement of interfacing analog devices to a computer through use of the computer's cartridge slot.
While many of the available ports of a computer could be used with an analog interface circuit, the cartridge slot was selected for this invention. A cartridge slot is an input port of a computer that is designed to let the computer read the contents of read only memories on the printed circuit board plugged into the cartridge slot. This arrangement allows both the reading of data or the reading of instructions for execution. The cartridge slot was selected for the following reasons:
(1) The other ports remain available for their intended purposes.
(2) The application program, the analog and switch interface circuit, and the interface driver program can all use the cartridge slot, requiring only one circuit board.
(3) The parallel data bit input arrangement and the integral software driver allows the design of a cost effective (simple) interface.